The present invention releates to a camera having a built-in electronic flash device, which allows photographing with the attachment of a detachable electronic flash device.
Among recent compact-sized cameras with 35 mm format photographic film, a camera type with a built-in flash device is the most popular, while many camera types with a built-in flash device are also nowadays found in the field of single-lens reflex cameras. For the above-mentioned cameras with a built-in flash device, however, the distance between the optical axis of the object lens and the light emitting section is limited due to the carrying ease thereof and a so called red-eye phenomenon may often occur, with high probability which is caused by reflection of flash light on human retinae as an object when the flash device is used.
It is known that the above-mentioned red-eye phenomenon is caused by normal reflection of flash light on the retinae of the object (human body) and the occurrence probability thereof depends upon the distance L between the optical axis of the lens and the light emitting section and the photographing distance D. The above-mentioned relation is shown in FIG. 4 for a case of L=60 and L=150, namely, the occurrence probability of the red-eye phenomenon is given as a function of the distance L and the photographing distance D. If the photographing distance D is constant, the longer the distance L between the optical axis of the photographing lens and the light emitting section, the occurrence probability of the red-eye phenomenon becomes lower. While the distance L is constant, the above-mentioned probability is reduced in accordance with the decrease of the photographing distance D. Furthermore, it is also known that in general the smaller the image magnification, it becomes much more difficult to identify the red-eye phenomenon even if occurred, while the red-eye phenomenon tends to occur more in dark places where human pupils are dilated, than in daylight places where human pupils are closed. In other words, the occurrence probability or conspicuousness of the red-eye phenomenon depends upon the above-mentioned photographing conditions.
For preventing the red-eye phenomenon, it is known to take the countermeasure in such manner that the camera body (including single-lens reflex cameras with a built-in flash device) is provided with an accessory shoe for another detachable flash device to be mounted thereon, so that the distance L between the light emitting section and the lens optical axis is increased. In such cases the detachable electronic flash device only is illuminated while the built-in electronic flash device is controlled in the inactivated condition.
U.S. Pat. No. 4,011,569 and Japanese Laid-Open Patent Publication No. 59-58425 are known as typical examples of the above-mentioned device. There is another type of camera of which built-in flash device can be activated even if a detachable flash device is attached, however, a selective control according to the photographing conditions is not provided for each of the built-in and detachable electronic flash device.
As described above, the control for activating not the built-in flash device but the detachable flash device only is somewhat effective in reducing the occurrence of red-eye phenomenon in dark places with high occurrence probability. It is to be noted, however, that the photographing conditions may be improved if both of the built-in and detachable flash devices are activated at the same time. For example, the activation of the both flashes can apply large guide number of the flash in conditions with low occurrence probability (conspicuousness) of the red-eye phenomenon, such as a comparatively bright place even in low brightness or a small image magnification with the use of a wide-angle lens. Moreover, the pupils of human eyes tend to be closed frequently even in back-light conditions at daytime so that the red-eye phenomenon does not occur, therefore, the activation of both flashes is useful for applying higher guide number.
On the other hand, if an object is found at a short distance (for example, more or less 2 m) in a dark place, the occurrence probability of red-eye phenomenon is about 10% at L=60 mm and the red-eye phenomenon does not often occur even if the built-in flash device is used. Moreover, if an object is found in a range for macro photography, a shift (parallax) appears for the orientation angle of the built-in flash device to the detachable flash device, as shown in FIG. 5, therefore, luminous intensity distribution becomes irregular if both flashes are activated at the same time. In such cases the control for activating the built-in flash device only with the detachable flash device kept off is useful in reducing the irregularity of the luminous intensity distribution and advantageous from the viewpoint of energy saving. As shown in FIG. 5, the distance between the built-in and detachable flash device becomes shorter, the above-mentioned irregularity tends to appear easier.